1. Field of the Invention
The present invention relates to an image determination apparatus for determining whether or not an image portion having a specific shape is contained in inputted image data, to an image search apparatus and to a computer readable recording medium storing an image search program.
2. Description of the Related Art
There are image forming apparatuses such as a copy machine, a facsimile machine, a printer, and a multifunctional peripheral having multiple functions thereof, which have functions of storing image data such as an inputted document image in a mass-capacity storage device and reading out and reprinting registration image data that has been inputted once at any time.
The function of reprinting is convenient. However, as an amount of the registered data increases, it is difficult to find data to be outputted. Accordingly, image search technology for searching for desired image data from a plurality of pieces of image data becomes important.
As an example of target image data for search, there is image data in which an image portion having a specific shape is contained. The term “specific shape” as used herein refers to the special mark having a specific shape such as a circle, a triangle or a quadrangle. In many cases, the circle in particular is a seal image and becomes a target for search. Therefore, techniques to determine whether or not an image portion circular in shape is contained are being developed. For example, the related art is disclosed in JP-A 62-137680 (1987).
Detection of a circular shape includes two main steps. As a first step, an edge that forms the circumference of a circle is detected. And as a next step, central coordinates and so on are determined based on the edge detected. Through these steps, the circle detection is performed.
For the detection of a circular shape, Hough transform is most commonly employed.
On the occasion of the detection of a circular shape, values to be determined are central coordinates and a radius. Consequently, the variable space becomes three dimensions including coordinates (x, y) and a radius r, and enormous computing quantity and storage capacity are required.
With the intention of resolving these problems, various detection methods which are improvements of Hough transform have been developed. However, sufficiently high detection accuracy still has not been achieved in the cases of containing, for example, complex images in the background of a circular image.
As other detection methods, there are a method of detecting a circular shape as a nonlinear curve without edge detection, a method of detecting a seal portion by a difference in colors between the seal portion and the other portions, and so on.
However, the detection as a nonlinear curve still requires enormous computing quantity and storage capacity, and the detection based on a difference in colors produces a problem in actual use because seal portions are various in their colors.
As mentioned above, the conventional methods for detecting a circular shape require enormous computing quantity and storage capacity. In addition, they have another problem that the image data used for detection is required to be free of stains and the like and to have a background image without a pattern.